Gallstone disease is a major health care concern in the United States. Recent clinical an experimental evidence has demonstrated that nutritional factors play an important role in gallstone pathogenesis. In this proposal, we will define the role of dietary calcium and caffeine, two important components of the American diet, in pathogenesis and prevention of gallstones. Our hypothesis for this proposal are that oral calcium supplementation promotes gallstone formation and that dietary caffeine may prevent gallstone formation. Preliminary results in the prairie dog appear to support these hypotheses but do not clearly explain the mechanism of these effects. In this proposal, we plan experiments which will confirm these observations and address a series of specific aims to define the exact mechanism by which calcium and caffeine exert their effect on gallstone formation. The specific aims of this proposal are to determine the role of dietary calcium and caffeine on: 1) Bile composition and bile flow. These experiments in the prairie dog model should determine changes in bile composition and secretion at both basal and bile salt-stimulated flow rates and should define for the first time in this model the kinetics of calcium secretion; 2) Gallbladder glycoprotein secretion. Glycoprotein secretion will be determined both in vivo in the prairie dog and in vivo in cultured gallbladder explants; 3) Bile nucleation. The effect of dietary calcium and caffeine on in vivo bile nucleation time will be determined for both prairie dog model bile systems; 4) Gallbladder absorption. Gallbladder mucosal absorption will be determined in an in vivo model by gravimetric determination and electrolyte flux; 5) Gallbladder motility. Prairie dog gallbladder motility will be determined by measuring cystic duct closing pressure, gallbladder emptying and pressure response to cholecystokinin, and cystic duct resistance; 6) Human bile composition and gallbladder emptying. Bile gathered by endoscopic aspiration will be analyzed biochemically and gallbladder emptying will be determined by quantitative radionucleotide scanning. These results should provide direct information concerning the effect of dietary calcium and caffeine on gallstone pathogenesis and prevention.